Microwave ovens usually comprise a cooking chamber in which food is placed to be heated, a magnetron for generating microwaves and a feeding port for feeding the microwaves into the cavity. A common problem associated with microwave ovens is that the heating provided by the microwaves is unevenly distributed within the cavity. This causes some parts of the food to be heated more rapidly than other parts. In other words, the heating results in food having regions of different temperatures (i.e. being more or less hot). For example, food that has been defrosted in a microwave oven often contains parts which are still frozen, while other parts of the food may be really hot. To ensure that all parts of the food in the microwave oven are properly heated, the user often heats the food for an extra long time, thereby running the risk of burning parts of the food because of overheating.
Several different approaches have been employed to overcome such a problem. A more even heating in a microwave oven may for example be obtained by placing the food on a turntable in the cavity. During heating, the turntable is rotated, whereby the heating provided by the microwaves is more evenly distributed in the food. However, the use of rotating turntables still does not provide sufficient spread of the heating in the food. Another drawback is that the introduction of extra moving parts such as the turntable, and a motor for driving the turntable, increases the risk of malfunction and also makes the microwave oven more complicated to manufacture.
Another approach for providing a more even heating is described in EP0788296 where a high frequency heating apparatus with local heating means capable of heating an optional portion of the food is disclosed. The local heating means provides a heating position that is changeable in a radial direction so that an optional portion of the food can be heated in association with rotation of a turntable on which the food is located. A uniform heating distribution of the food may then be obtained by a combined heating of optional portions. Although this high frequency heating apparatus may provide better control of the heating than those only using turntables, it is fairly complicated and still requires a turntable and a motor for rotating the turntable.
Thus, there is a need for new apparatus and methods that would overcome, or at least alleviate, some of the above mentioned drawbacks.